The diagnostic characteristics of autism spectrum disorder (ASD) includes challenges in social communication skills. Among different components of social communication, language, particularly vocabulary, must be supported early in children's development as language is shown to be associated with academic, social, cognitive, and adaptive skills and their development trajectory. Enhanced milieu teaching (EMT) is one of evidence-based, naturalistic interventions that are designed to support the vocabulary development of young children with ASD. EMT is often implemented by caregivers, therapists, or teachers; however, there is no study that evaluated the effectiveness of sibling-implemented EMT on the vocabulary use of children with ASD. With the rise of COVID-19, there is an increased duration of family interactions at home which led to the need for more structured and effective strategies for social interactions, especially for children with ASD. As siblings frequently engage in social interactions such as play, training older siblings to facilitate effective communication and play with their younger siblings with ASD could improve the language development of children with ASD as well as the siblings' social interactions. Adapting a multiple probe design, the study examined the effects of sibling-implemented EMT with virtual performance feedback for the siblings without ASD on the siblings' implementation fidelity of EMT and language outcomes and percentage of responses by children with ASD. Generalization with a novel material and maintenance over one week, two weeks, or one month was measured. Social validity questionnaires were completed by the siblings and the caregivers after the intervention. The findings provide implications for family-centered evidence-based practices, particularly through the use of virtual training for family members including the siblings of children with ASD. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]